Plasmodium falciparum, the causative agent of human malaria, undergoes distinct morphological changes during the progression through its life cycle in the mosquito and human hosts. During the intraerythrocytic life cycle, the parasite diverges from the paradigm of eukaryotic cell cycle by undergoing multiple rounds of DNA replication and forms 8 to 32 merozoites from a single cell. A clear understanding of the biochemical changes and molecular switches that regulate the unusual erythrocytic developmental stages of the malaria parasite has not been established. The long-term goal of this research is to develop a model for cell cycle regulation in the intraerythrocytic stages of development of malaria parasite P. falciparum. The regulation of the precise timing of initiation of DNA synthesis and the relationship between S phase and mitosis during development in P. falciparum remains unclear, as does the identity of the proteins involved in cell cycle progression and how the are regulated. Recent research done in our laboratory has identified a few molecular tools to initiate an in-depth study of the cell cycle regulation of P. falciparum. Specifically, we propose to carry out the following: (a) To identify and characterize components of P. falciparum pre-replication complex, we will initially focus on cell cycle regulated changes in expression, intracellular localization, and phosphorylation of P. falciparum homologues of MCM4, ORC1 and ORC5. (b) Identify proteins interacting with P. falciparum CDK-like kinases, CDK- activating kinases and pre-replication complex components by phage- based interaction cloning, phosphorylation screen of a lambda screen library, and by two-hybrid screen. (c) Develop more effective means of cell cycle synchronization of the parasites. A detailed analysis of P. falciparum cell cycle regulators provide insight into the molecular mechanism of unusual asexual division during Plasmodium schizogony. Furthermore, enzymes involved in cell cycle progression have the potential to be attractive targets for drug development, especially given that differences between cell cycle regulation in parasite and host might permit a level of specificity in directing therapies against the parasite.